Process of recovering metals by electrolysis.



cyclical.

UNITED STATES PATENT OFFICE.

LAWRENCE ADDICKS, OF DOUGLAS, ARIZONA.

PROCESS OF RECOVERING METALS BY ELECTROLYSIS.

No Drawing.

To all whom it may concern:

Be it known that I, LAWRENCE ADDIoKs, a citizen of the United States of America, residing in Douglas, in the county of Cochise and State of Arizona, have invented certain new and useful Improvements in .Processes of Recovering Metals by Electrolysis, of which the following is a specification.

This invention relates to a process of electrolysis, more especially to the electrolysis of copper, and aims to provide improvements therein.

In the electrolysis of metals, and in particular copper, the presence of certain compounds of metals other than that to be deposited, occurring in the electrolyte or formed therein .hy the reaction occurring during the electrolysis, exercisesa solvent action on the deposited metal, which is often detrimental. For instance, copper ores usually contain iron, and when the copper ore is dissolved, iron compounds are also dis solved, and are mixed with the copper compounds inthe liquid. Or, iron compounds may be introduced in the electrolyte for the purpose of depolarizing. When these iron compounds are in the -ous state they will be oxidized to the -i0 state by the action occurring at the anode. Ferric compounds are, reduced by cop er, and conse-" quently the ferric compoun s occurring in the electrolyte would act to dissolve the deposited copper.

Ferric salts have in fact lon been known as active oxidizing agents a'p icable to. the lixiviation of the mineral valiies in certain ores. Well-known processes, such as that commonly known as the Siemens-Halske,

have been evolved where ferrous sulfate is converted into ferric sulfate by anodic oxidation in an electrolytic cell, the corresponding cathodic reduction being'used to deposit copper in this case, the depleted and oxidized electrolyte being returned to the lixiviation tanks, thereby making the process The f. rous sulfate at the same time acts as a depolarizer in the cell, the equivalent of the emical energy of anodic oxidation appearing as a corresponding lowering of voltage under proper conditions of operation.

The great difliculty in such processes is in keeping the ferric sulfate formed from attacking and redissolving the cathodes thereby wholly orin part making the useful Specification of Letters Patent.

Patented May 11, 1915.

Application filed November 5, 1914. Serial No. 870,440.

yield of the cell too low for commercial purposes. Two methods have been. proposed to oyercome this (a) the use of a mechanical diaphragm to keep the anolyte and catholyte separate; and (b) the injection of sulfur dioxid' gas into the cell' which is in effect a chemical diaphragm in that it reduces the ferric salt to the ferrous salt, at the same time being itself oxidized to sulfuric acid; it also partly displaces the ferrous salt as a depolarizer, being itself oxidized tosulfuric acid directly at the anode. The first plan is open to many mechanical and electrical obfect1ons and has not found general favor}. The second vitiates the atmosphere of the cell room, is limited to an ore which can be economically leached by sulfuric acid, and requlres a somewhat prodigal use of sulfur dlOXld 1n order to attain the desired result.

I have found that the activity of the -metal compounds which exercise a solvent I deposited metal to attack; (d) the surface of the deposited metal exposed, and (e) the concentration of other salts in the solution.

It is evident that .within certain limits, (at), (b), (0), and (d) can be favorably balanced by the choice of a suitable rate of circulation through the cell, current density, etc., but (e) is the controlling factor.

In general the presence in quantity of a compound or compounds other than that of the metal to be deposited in such an electrolyte as referred to, that is, one containing a compound ofthe metal to be deposited and a compound exercising a solvent action on the deposited metal, seems to have a deter-I rent eflect on the activity of the solvent compound, this being very markedly so in the case of aluminum sulfate. I therefore use in a cell, a sulfate copper electrolyte for example, with sufiicient cupric sulfate and ferrous sulfate present to give a good deposit of copper at the cathode and efiicient depolarization at the anode (anodic oxidation) for the circulation used. I also use sufiicient aluminum sulfate to retard the corrosion rate at the cathode to a small proferric sulfate by other means when it is desired to utilize, outside of the cell, the solution containing the ferric sulfate. As a practical illustration I finu a suitable set of conditions for good work to be, using a carbon anode and copper cathode, a solution containing copper, iron and aluminum salts, all as sulfates, showing on analysis 3% copper, 3% ferrous iron and 3% alumina, some free sulfuric acid to prevent the formation of basic salts, a current density of 13.5 amperes per, sqsft, a temperature of 115 F. and acirculation sufficient to hold the average concentration of ferric iron present to about 0.25%. Under such conditions a cathode deposit equivalent to from 70% to 90% of the theoretical can be obtained.

After leaving the cells the solution can be used direct upon ores containing native copper such as the tailings dumps in Michigan, which carry lake mineral, or for extracting the finely divided copper contained in anode slimes from copper refining preparatory to their treatment for the recovery of. silver and gold by well known processes. In these cases the lessened activity of the reaction due to the presence of aluminum and other sulfates is compensated for by the great surfaceexposed by the fine state of subdivision in which the copper exists. The reduction is thorough and 90% current efficiency should be obtained.

Certain sulfid ores may also be attacked directly, but it is generally advisable to give these a preliminary roast, thereby transferring them to the oxidized class.

Inthe case of oxid ores, the ferric sulfate may be reduced by suitable means such as sulfur dioxid gas, resulting in the formation of sulfuric acid which is used as the leaching agent for oxids, silicate and carbonates of copper, the sulfate being directly soluble in water. Theoretically a free acid yield of about three pounds per lb. of

- copper deposited can be obtained in this way, half being supplied by the ferric sulfate reduced and half by the sulfurous acid oxidized. When the gas is weak'in S0 owing to its being a by-product from roasting, it may be diflicult to obtain complete reduction so that some iron sulfate enters the cell unreduced making it difficult to keep the average ferric iron in the cell down to the desired point, resulting in an undesirably low current efficiency. In such cases a certain proportion of the copper leached maybe cemented upon iron, the electrolyte leaving the cells first being subjected to the action of the SO, and then to that of the cement copper. This will properly reduce the solution and restore the cell efficiency. Gementation at the same time afi'ords a means of lowering the electrolyte in salts. composition of the electrolyte mustbe main The I tained in'any case by systematic additions and withdrawals, the ore generall furnishing the desired source of alumina and iron, as well as of copper.

What is claimed is:

1. In a process for the electrolytic reduction of metals in the presence of a substance having a solvent action. upon the deposited metal, electrolyzing in the presence of a salt adapted to counteract the solvent action of said substance having the dissolving action.

2. In a process for the electrolytic reductionof metals in the presence of a substance having a solvent action upon the deposited metal, electrolyzing in the presence of a sulfate adapted to counteract the solvent action of said substance having the dissolving action.

3. In a process for the electrolytic reduction of metals in the presence of a substance having a solvent action upon the deposited metal, electrolyzing in the presence of aluminum sulfate of a concentration adapted to counteract the solvent action of said substance having the dissolving action.

4:. In a process for the electrolytic reduction of metals in the presence of a substance having a solvent action upon the deposited metal, electrolyzing in the presence of a substance adapted to counteract the solvent action of said substance having the dissolving action, said counteracting substance being present in amount sufficient to materially reduce the degree of attack on the cathode and yet insufficient to deaden its effect, whereby the solution may be sufiiciently used as a solvent for metals or ores.

5. In a process for the electrolytic reduction of copper in the presence of a depolarizer which acts to form a substance having a solvent action upon the deposited copper, electrolyzing in the presence of a salt adapted to counteract the solvent action of said substance having the dissolving ac'- tion.

6. In a process for the electrolytic reduc tion of copper in the presence of an iron salt having a solvent action upon the deposited copper, electrolyzing in the presence of a salt ada ted to counteract the solvent action of the iron salt. y

7. In a process for the electrolytic reduction ofcopper in the presence of an iron salt having a solvent action upon the deposited copper, electrolyzing in the presence of aluminum sulfate of a concentration adapted to counteract the solvent action of said iron salt. 1

-8. In a process for the electrolytic reduction of copper in the presence of an iron salt having a solvent action upon the de posited copper, electrolyzing in the presence of aluminum sulfate adapted to counteract the solvent action of said iron salt, said aluminum sulfate being present in amount sufficient to materially reduce the degree of-;"

attack on the cathode and yet insufficient to deaden the leaching efiect of the solution.

9. In a process for the electrolytic reduction of copper, electrolyzing in the presence of a ferrous compound adapted to operate as a depolarizer, and in the presence of a substance adapted to counteract the solvent action of the ferric compound formed in the electrolyte.

10. In a process for the electrolytic reduction of copper, electrolyzing in-the presence of a ferrous salt adapted to operate as a depolarizer, and in the presence of a substance adapted to counteract the solvent action of the ferric salt formed in the electrolyte.

11. In a process for the electrolytic reduction of copper, electrolyzing in the presence of a ferrous salt adapted to operate as a depolarizer, and in the presence of a salt adapted to counteract the solvent action of the ferric salt formed in the electrolyte.

12. In a process for the electrolytic reduction of copper, electrolyzing in the presence of a ferrous salt adapted to operate as a depolarizer, and in the presence of aluminum sulfate of a concentration adapted to counteract the solvent action of the ferric salt formed in the electrolyte.

13. In a process for the electrolytic reduction of copper, electrolyzing in the presence of a ferrous salt adapted to operate as a depolarizer, and in the presence of a substance adapted to counteract the solvent action of the ferric salt formedin the electrolyte, said counteracting salt being present in amount sufficient to materially reduce the degree of attack on the cathode and yet insuflicient to deaden the leaching effect of the solution.

14. In a process for the electrolytic reduction of metals in the presence of a substance having a solvent action upon the deposited metal, electrolyzing in the presence of a substance adapted to counteract the solvent action of said substance having the dissolving action, and using portions from the bath for the dissolving of metal compounds to be electrolyzed.

15. In a process for the electrolytic reduc tion of copper in the presence of a salt having a solvent action upon the deposited copper, electroly zing in the presence of a salt adapted to counteract the solvent action of said salt having the dissolving action, and using portions from the bath for-the dissolving of metal compounds to be electro lyzed.

16. In a process for the electrolytic reduction of copper, electrolyzing in the presence of a ferrous salt adapted to operate as a depolarizer, and'in the presence of a substance adapted to counteract the solvent action of the ferric salt formed in the electrolyte, and using portions from the bath for the dissolving of copper compounds to be electrolyzed.

17. In a process for the electrolytic reduction of copper, electrolyzing in the presence of a ferrous salt adapted to operate as a depolarizer, and in the presence of aluminum sulfate of a concentration adapted to counteract the solvent action of the ferric salt formed in the electrolyte, and using portions from the bath for the dissolving of copper compounds to be electrolyzed.

In. Witness whereof, I have hereunto signed my name in the presence of two subscribing Witnesses.

LAWRENCE ADDICKS.

Witnesses GEORGE FORDHAM, KATHERINE CONKLIN. 

